1. Field of the Invention
The present invention relates to a colorimetric chart, and a color reproduction estimating device.
2. Description of the Related Art
In image forming apparatuses such as printers or multifunction products, in order to form a surface image on a target medium for image formation, the medium is moved in a direction (sub-scanning direction) that is perpendicular to a constant direction (main-scanning direction) in which an image is formed in a linear manner or a belt-like manner. At that time, periodical concentration fluctuation, attributed to the configuration of the image forming apparatus, occurs in the sub-scanning direction.
Such concentration fluctuation in the sub-scanning direction becomes the cause of a measuring error regarding a colorimetric chart used in gradation characteristic calibration or regarding a colorimetric chart used in obtaining a color reproduction characteristic model that enables performing color management.
Generally, in office printers, electrophotographic photosensitive drums having diameter in the range of about φ30 mm to φ40 mm are used; while in high-speed printers of the 100 ppm category (where ppm stands for page per minute), electrophotographic photosensitive drums having diameter in the range of about φ60 mm to φ100 mm are used. Thus, in synchronization with the eccentricity of the photosensitive drums, the concentration fluctuation in the sub-scanning direction occurs in the range of about 90 mm to 300 mm. That is, for the width of 297 mm in A4 portrait format, about 1 to 3 cycles of periodic fluctuation occurs (for A4 landscape format), and about 0.5 to 1.5 cycles of periodic fluctuation occurs (for portrait format).
From among the periodic concentration fluctuation occurring on a formed image, the fluctuation components of the short-term concentration fluctuation in the order of a few mm can be eliminated to an extent by the randomization of measurement patch arrangement or by performing the statistical processing. That helps in reducing the abovementioned measuring error regarding a colorimetric chart.
Meanwhile, regarding the long-term concentration fluctuation having the cycle of several tens of pages, a colorimetric chart having the total color measurement of about 1 to 4 pages can be used so that it becomes possible to obtain a model for estimating color reproducibility for the measurement data. However, regarding the medium-term concentration fluctuation of about several cycles within one page, randomization of the patch arrangement that constitutes a chart does not result in sufficient elimination of the fluctuation components. Moreover, sufficient uniformity is also not achieved for modeling the color reproduction characteristic.
Japanese Patent Application Laid-open No. 2007-264364 can be cited as a conventional technique for tackling the issue of periodical concentration fluctuation in the sub-scanning direction. In Japanese Patent Application Laid-open No. 2007-264364, at the half cycle of the concentration fluctuation cycle, patches specified to have the same concentration gradation value are arranged and are to be measured so as to counterbalance the amount of periodical fluctuation in the sub-scanning direction of the concentration to be managed.
However, in the technique disclosed in Japanese Patent Application Laid-open No. 2007-264364, although the effect of fluctuation can be eliminated by averaging the concentration detection value detected at the half cycle of the fluctuation cycle, it is not possible to estimate and correct the periodic fluctuation.